📘 English Definition（英文释义）
- A straight line (or the length of such line)
- connecting any point, as of a curve, with a fixed point, or pole, round
- which the straight line turns, and to which it serves to refer the
- successive points of a curve, in a system of polar coordinates. See
- Coordinate, n.
- n. An ideal straight line joining the center of an
- attracting body with that of a body describing an orbit around it, as a
- line joining the sun and a planet or comet, or a planet and its
- satellite.